Pure rabbit pulmonary angiotensin-converting enzyme will be cleaved with cyanogen bromide and proteolytic enzymes. Peptide fragments will be isolated and characterized with respect to amino acid composition and sequence. Antiholoenzyme antibody will be fractionated into populations specifically directed at the defined pDptide fragments. Identification of the membrane orientation of the enzyme polypeptide and of its active site will be attempted using these fragments and antibodies. The effects of passive and active immunization against converting enzyme on the blood pressure of normal and hypertensive rabbits and dogs will be examined. General physiologic functions of dipeptidyl carboxypeptidase will be investigated by comparing the properties of wild type E. coli and mutants of it which lack this activity. Isolation and purification of mRNA coding for rabbit pulmonary converting enzyme will be attempted. A comparison will be made of the polypeptide chain of the enzyme as isolated and as synthesized in the wheat germ system programmed by the RNA template.